Polycarbonate polymers are known as being excellent molding materials since products made therefrom exhibit such properties as high impact strength, toughness, high transparency, wide temperature limits (high impact resistance below -60.degree. C. and a UL thermal endurance rating of 115.degree. C. with impact), good dimensional stability, good creep resistance, and the like. It would be desirable to add to this list of properties those of low water vapor transmission and low gas permeability to enable the aromatic polycarbonates to be used, among other applications, to form containers and film wraps for foods, beverages, cosmetics, and the like. In particular, food and beverage containers made from aromatic polycarbonates having these added barrier properties would be more economical as they would be capable of reuse and would thus also help reduce the impact of environmental waste occasioned by broken glass and discarded, non-reusable containers.
Under certain conditions, such containers and film wraps can be used for materials whose exposure to fire hazard should be minimized. Therefore, it would also be desirable to impart to these containers and film wraps the additional property to flame resistance or fire retardance without sacrificing low water vapor transmission and low gas permeability properties.
It is known to obtain polycarbonates that contain halogenated monomers as their main, polymeric building blocks. For example, U.S. Pat. No. 3,062,781 discloses flame retardant halogenated polycarbonates but the only dihalogenated diphenol disclosed is dichlorobisphenol-A as all the other halogenated diphenols disclosed are tetrahalogenated diphenols. The statement is made that the halogenated polycarbonates obtained from these halogenated diphenols also show "reduced permeability to steam" and that "these properties are the more distinct the higher the halogen content is of the new polycarbonates" (Col. 5, lines 16 and 18-19).
U.S. Pat. No. 3,312,659 discloses a dichloromethylene bisphenol polycarbonate but does not include data characterizing the polymer.
U.S. Pat. No. 3,312,662 discloses the ester chloride of a dichlorinated polycarbonate, but also does not include data characterizing the polymer.
German Pat. No. P25 20 317.2 discloses that halogenated polycarbonates can be obtained from preparing halogenated monomers containing mixtures of unreacted bisphenols and statistical mixtures of halogenated bisphenols. The halogenated bisphenols comprise, primarily, tri- and tetrahalogenated bisphenol.
In general, these prior art references recognize that flame retardance can be imparted to polyesters by halogenating the monomeric building blocks from which they are obtained.